A radio link control (RLC) entity in a wireless transmit/receive unit (WTRU) and UMTS terrestrial radio access network (UTRAN) may operate in a transparent mode (TM), an unacknowledged mode (UM), or an acknowledged mode (AM). An UM RLC entity and a TM RLC entity may be configured to be a transmitting RLC entity or a receiving RLC entity. The transmitting RLC entity transmits RLC protocol data units (PDUs) and the receiving RLC entity receives RLC PDUs. An AM RLC entity comprises a transmitting side and a receiving side. The transmitting side of the AM RLC entity transmits RLC PDUs and the receiving side of the AM RLC entity receives RLC PDUs.
FIGS. 1A and 1B show conventional UM and AM RLC PDU formats, respectively. The Sequence Number fields indicate the sequence number of the RLC PDU. The Length Indicator fields are used to indicate the last octet of each RLC service data unit (SDU) ending within the RLC PDU. RLC SDUs or segments of RLC SDUs are mapped to the Data field.
Conventionally, an AM RLC entity may generate RLC PDUs of a fixed size in the uplink (UL) that is configured by the network via radio resource control (RRC) signalling. Similarly, an UM RLC entity may choose the RLC PDU size from a limited configured set of sizes.
In the Third Generation Partnership Project (3GPP) Release 7, the RLC protocol has been extended to support flexible RLC PDU sizes in the down link (DL), but not in the UL. In 3GPP Release 8, the flexible RLC PDUs are allowed in the UL as well so that the AM and UM RLC entities are allowed to create RLC PDUs of a flexible size in the UL.
The network may configure an uplink radio bearer in a wireless transmit/receive unit (WTRU) to generate RLC PDUs of a flexible size within a minimum and maximum RLC PDU size, which are configured by the RRC layer. More specifically, the WTRU may segment and/or concatenate uplink RLC SDUs to create RLC PDUs larger than or equal to a minimum UL RLC PDU size and smaller than or equal to a maximum UL RLC PDU size. If data to be transmitted is not large enough to create an RLC PDU of the minimum UL RLC PDU size, the RLC entity may create an AM PDU smaller than the minimum UL RLC PDU size. This removes the need for padding in a case where the amount of available data is lower than the minimum UL RLC PDU size.
For maximum transmission efficiency, the size of the RLC PDU should match the number of bits that will be allowed to be sent over the air interface in the current transmission time interval (TTI) for a given logical channel. This increases transmission efficiency and greatly reduces layer 2 (L2) header overhead.
Under the current 3GPP specification, the RLC entity may create RLC PDUs at a given transmission opportunity based on the number of bits requested for the given logical channel from the medium access control (MAC) entity. The RLC entity selects the size of the data field of the RLC PDU to match the data requested for a particular logical channel by the MAC entity. With this option, the RLC entity needs to wait until the transmission opportunity to get the information from the MAC entity and, therefore, some latency issue may occur.
Alternatively, the RLC entity may create more RLC PDUs than what may be transmitted at the upcoming TTI. This option relaxes the processing requirements since this effectively creates a delay between the creation of an RLC PDU and its inclusion in a MAC PDU. The size of the RLC PDU is based on number of bits allowed to be transmitted according to the current grant, scheduled or non-scheduled.
In order to further improve the wireless system throughput, multi-carrier operation is being considered in 3GPP. In multi-carrier operation, the WTRU and the Node-B may transmit and receive via multiple carriers.
The flexible RLC PDU creation currently handles the case where RLC PDUs are transmitted via a single carrier. The inventors have recognized that, with multi-carrier operation, a WTRU will have the option to transmit more than one MAC PDU in a given TTI via multiple carriers. Since the channel conditions, available power, and grant may not be the same over the carriers, techniques for flexible PLC PDU creation for multi-carriers are required.